Methods for anisotropic control of selective silicon removal

ABSTRACT

Embodiments of the present technology may include a method of etching. The method may include flowing a gas through a plasma to form plasma effluents. The method may also include reacting plasma effluents with a first layer defining a first feature. The first feature may include a first sidewall, a second sidewall, and a bottom. The first sidewall, the second sidewall, and the bottom may include the first layer. The first layer may be characterized by a first thickness on the sidewall. The method may further include forming a second layer from the reaction of the plasma effluents with the first layer. The first layer may be replaced by the second layer. The second layer may be characterized by a second thickness. The second thickness may be greater than or equal to the first thickness. The method may also include removing the second layer to expose a third layer.

TECHNICAL FIELD

The present disclosure applies broadly to the field of semiconductor processing. More specifically, methods for radical etching of layers are disclosed.

BACKGROUND

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers, or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process that etches one material faster than another facilitating, for example, a pattern transfer process. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits, and processes, etch processes have been developed with a selectivity towards a variety of materials.

Dry etches produced in local plasmas formed within the substrate processing region can penetrate more constrained trenches and exhibit less deformation of delicate remaining structures than wet etches. However, even though an etch process may be selective to a first material over a second material, some undesired etching of the second material may still occur.

Thus, there is a need for improved systems and methods that can be used to produce high quality devices and structures. These and other needs are addressed by the present technology.

BRIEF SUMMARY

Embodiments of the present technology may allow for improved performance and reliability of semiconductor devices. Embodiments may reduce unwanted etching near critical features of semiconductor devices by partially or fully blocking etchants from reaching the bottom of a trench or via. Etchants may be blocked by forming a solid etch byproduct. The solid etch byproduct may form a protective layer that does not get etched by the etchants. Embodiments may result in an anisotropic etch rather than an isotropic etch. Embodiments of the present technology may also reduce the possibility of overhang at the top of a trench or via by preferentially etching the top of the trench or via.

Embodiments of the present technology may include a method of etching. The method may include flowing a gas through a plasma to form plasma effluents. The method may also include reacting plasma effluents with a first layer defining a first feature. The first feature may include a first sidewall, a second sidewall, and a bottom. The first sidewall, the second sidewall, and the bottom may include the first layer. The first layer may be characterized by a first thickness on the sidewall. The method may further include forming a second layer from the reaction of the plasma effluents with the first layer. The first layer may be replaced by the second layer. The second layer may be characterized by a second thickness. The second thickness may be greater than or equal to the first thickness. The method may also include removing the second layer to expose a third layer. The third layer may define a second feature.

Embodiments of the present technology may include a method of etching. The method may include flowing a gas through a plasma to form plasma effluents. The method may also include reacting plasma effluents with a polysilicon layer defining a first trench. The first trench may include a first sidewall, a second sidewall, and a bottom. The first sidewall, the second sidewall, and the bottom may include the polysilicon layer. The polysilicon layer may be characterized by a first thickness on the first sidewall. The method may further include forming a first solid layer from the reaction of the plasma effluents with the polysilicon layer. The polysilicon layer may be replaced by the first solid layer. The first solid layer may include (NH₄)₂SiF₆. The first solid layer may be characterized by a second thickness. The second thickness may be greater than or equal to the first thickness. The method may include removing the first solid layer to expose a remaining portion of the polysilicon layer. The remaining portion of the polysilicon layer may define a portion of a second trench.

Embodiments of the present technology may include a method of etching. The method may include flowing a gas through a plasma to form plasma effluents. The method may also include reacting plasma effluents with a first layer defining a first trench. The first feature may include a first sidewall, a second sidewall, and a bottom. The first sidewall, the second sidewall, and the bottom may include the first layer. The first layer may be characterized by a first thickness at a first position on the first sidewall. The first layer may be characterized by a second thickness at a second position above the first position on the first sidewall. The method may further include forming a second layer from the reaction of the plasma effluents with the first layer. A portion of the first layer may be replaced by the second layer. In addition, the method may include removing the second layer to expose a remaining portion of the first layer and to define a second trench. The remaining portion of the first layer may be characterized by a third thickness at the first position on the first sidewall. The remaining portion of the first layer may be characterized by a fourth thickness at the second position on the first sidewall. The fourth thickness may be greater than the third thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional process of etching according to embodiments.

FIG. 2 shows a process flow of etching according to embodiments of the present technology.

FIG. 3 shows a method of etching according to embodiments of the present technology.

FIG. 4 shows a method of etching according to embodiments of the present technology.

FIG. 5 shows a process of etching according to embodiments of the present technology.

FIG. 6 shows a method of etching according to embodiments of the present technology.

FIG. 7 shows a top plan view of one embodiment of an exemplary processing tool according to embodiments of the present technology.

FIG. 8 shows cross-sectional views of an exemplary processing chamber according to embodiments of the present technology.

DETAILED DESCRIPTION

As characteristic dimensions decrease, the negative effects of process defects on performance and reliability increases. For example, FIG. 1 shows that a conventional process may result in a leakage path. Substrate 102 has electrically active areas 104 and 106. Substrate 102 may be a silicon wafer, and electrically active areas 104 and 106 may include silicon germanium and/or silicon phosphorous. A trench is defined by a polysilicon cap 108 on a high-k dielectric layer 110. The high-k dielectric layer may be adjacent to a spacer 112, which may be adjacent to layer 114. A processing defect may be present in the bottom of the trench, which may cause an undesired deposit 116 of polysilicon. In a conventional etch of polysilicon, polysilicon cap 108 may be etched away. However, undesired deposit 116 may also be etched, which may lead to parts of electrically active area 106 being etched away, resulting in void 118. Void 118 may cause poor device performance including shorting or no electrical connections.

FIG. 1 is only one example of possible defects resulting from conventional processes. With FIG. 1 and other situations, an anisotropic etch, instead of an isotropic etch, may be desired. For example, the sidewalls may not be etched at the same rate as the top or the bottom of a trench. Processing material may need more stringent processing constraints near the bottom of a trench or via, where underlying layers contain sensitive parts of a semiconductor device. Embodiments of the present technology may intentionally minimize the amount of processing near the bottom of a trench or via. One method to anisotropically etch or to minimize the processing near the bottom is to form a solid etch byproduct, rather than a gaseous etch byproduct.

I. Layer Removal Using Solid Byproduct

A. Process Flow

FIG. 2 shows a process flow according to embodiments of the present technology. The leftmost image in FIG. 2 is the same as the leftmost image in FIG. 1. However, instead of a conventional etch involving forming a gaseous etch byproduct, a solid byproduct layer 140 is formed. Solid byproduct layer 140 blocks off additional plasma effluents from etching too deeply into the polysilicon. For example, part of undesired deposit 116 is replaced with solid byproduct layer 140. However, much of undesired deposit 116 remains unetched and unconverted to solid byproduct layer 140. The solid byproduct layer 140 can be removed by annealing or sublimating, resulting in the rightmost image in FIG. 2. Some undesired deposit 150 remains, and electrically active area 106 is not etched by the removal of polysilicon cap 108. The resulting device may result in better performance and reliability than a device formed with a conventional etch that may have a void 118 as in FIG. 1.

B. Solid Byproduct Formation

The solid byproduct formed when etching polysilicon may be (NH₄)₂SiF₆. Certain processing conditions may aid in forming this solid byproduct. Gases used for etching polysilicon may include at least one of F-containing gas (e.g., NF₃, F₂, or HF), a H-containing gas (e.g., H₂, NH₃, or an amine). Even if there is no NH₃ precursor, NH₃ can be generated from one or more N-containing gases and one or more H-containing gases under certain condition which can then from the solid byproduct from silicon etch. To form the solid byproduct, NF₃ may have to be first replaced with NH₃. Increasing the formation of NH₃ may increase the formation of solid byproduct (NH₄)₂SiF₆.

More NF₃ would tend to produce more NH₃ as more NF₃ supplies more nitrogen atoms for NH₃ formation. Increasing the pressure may increase radical collision possibility and may therefore increase NH₃ formation. Lower pedestal temperature may increase the solid byproduct formation by reducing sublimation. The solid byproduct may sublimate at temperatures above 80° C. In situations similar to FIG. 2, increased NF₃ flowrate, higher pressure, and lower pedestal temperature may improve the process and final device.

In some embodiments, the solid byproduct formed may include a halide atom other than fluorine. For example, the solid byproduct formed may include (NH₄)₂SiX₆, where X is a halogen (i.e., F, Cl, Br, I, At). For example, X may be a chlorine atom when (NH₄)₂SiCl₆ is a solid byproduct formed from etching silicon. Gases may include any halogen-containing gas (instead of a F-containing gas) and any gases described herein.

To remove the solid byproduct, the substrate with the solid byproduct may be annealed. Annealing may raise the temperature of the solid byproduct so that the solid byproduct sublimates into a gas, exposing the underlying layer. In situ annealing may be done between two etches or after an etch. In situ annealing may remove solid byproduct from the bottom of the trench.

C. Example Methods

As shown in FIG. 3, embodiments of the present technology may include a method 300 of etching. Method 300 may include flowing a gas through a plasma to form plasma effluents (block 302). The gas may include at least one of a F-containing gas (e.g., NF₃, F₂, or HF), a H-containing gas (e.g., H₂, NH₃, or an amine), a N-containing gas (e.g., N₂), an inert gas, or any gases described herein. The plasma effluents may include NH₃ and any other effluents described herein. The plasma may be maintained with an RF power of 5 to 1500 W, including 5 to 500 W, 500 W to 1000 W, and 1000 W to 1500 W.

Method 300 may also include reacting plasma effluents with a first layer defining a first feature (block 304). The first layer may be on a semiconductor substrate, which may include a semiconductor wafer or may include a semiconductor wafer with additional layers on top of the semiconductor wafer. The first layer may include silicon, including polysilicon. The first layer may be polysilicon cap 108 in FIG. 2. The first feature may include a first sidewall, a second sidewall, and a bottom. The first sidewall, the second sidewall, and the bottom may include the first layer. The first layer may be characterized by a first thickness on the sidewall. The first thickness may be the mean or median thickness on the sidewall. The first thickness may be in a range from 15 Angstroms to 300 Angstroms, including from 15 to 50 Angstroms, 50 to 100 Angstroms, 100 to 150 Angstroms, 150 to 200 Angstroms, and 200 to 300 Angstroms. The first feature may be a trench or via characterized by a height. The height may be a first height before reacting plasma effluents with the first layer. In FIG. 2, the first thickness may be the width of polysilicon cap 108 at the side of the trench.

In this description, position of layers may be described as bottom, top, above, below, and other directional terms. These terms are used with the understanding that the substrate is oriented as in the figures and the terms are relative to the substrate, not toward the center of the earth. One of skill would understand that the substrate could be flipped over but the directional terms would not describe different parts of a feature.

Reacting plasma effluents with the first layer may be at a pressure greater than or equal to 0.5 Torr, greater than or equal to 1 Torr, greater than or equal to 2 Torr, greater than or equal to 3 Torr, or greater than or equal to 4 Torr. Reacting the plasma effluents with the first layer may be at a temperature of less than or equal to 70° C., 60° C., 40° C., 30° C., 20° C. and/or greater than or equal to 0° C., 10° C., 20° C., 30° C., 40° C., 50° C., or 60° C. The pedestal may be set at any temperature described herein.

Method 300 may further include forming a second layer from the reaction of the plasma effluents with the first layer (block 306). The first layer may be replaced by the second layer. The second layer may be solid byproduct layer 140 in FIG. 2. The second layer may be characterized by a second thickness. The second thickness may be greater than or equal to the first thickness. The second thickness may be greater than two times the first thickness, three times, or four times the first thickness. Forming the second layer may include defining a feature such as a trench or via and may be the same type of feature as the first feature. Forming the second layer may include reducing the height of the trench or via from the first height to a second height. In some embodiments, forming the second layer may fully block the opening of the trench or via. In embodiments, forming the second layer may fill the space previously defined by the trench or via, such that no trench or via is evident after the second layer is formed. In other embodiments, fully blocking the opening of the trench or via may block the opening at the top, but not fully fill the space previously defined by the trench or via. For example, the solid byproduct may form a particle-like structure lodged at the top of the trench or via but may leave space below the structure.

The second layer may include (NH₄)₂SiF₆. The second layer may include N—H and/or Si—F bonds. The second layer may be a solid. The second layer may be a product of a reaction between ammonia, silicon, and/or plasma effluents.

One of skill would understand that the second layer formed in these embodiments is different from any layers formed on sidewalls during reactive ion etching (ME) or similar processes. The layers formed in ME etching are often thin, include carbon and fluorine, and are deposited from gas phase reactions instead of converted from a solid layer. In addition, RIE does not coat the bottom of the trench during etching, unlike the solid byproduct formation in these embodiments.

Method 300 may also include removing the second layer to expose a third layer (block 308). The third layer may define a second feature. The third layer may be high-k dielectric layer 110. The second feature may include a third sidewall. The second layer may be characterized by a second thickness on the third sidewall. The second feature may be a trench or via and may be the same type of feature as the first feature. The trench or via may define an opening. The opening may be characterized by a width of less than 15 nm, 10 nm, or 8 nm. The third layer may include TiN and/or hafnium oxide. The second feature may be the first feature with the first layer removed.

Removing the second layer may include increasing the temperature of the second layer to 70° C. or greater, including a range from 70° C. to 150° C. Removing the second layer may be by an in situ anneal. In other words, the second layer may be annealed without removing the substrate from the chamber. A showerhead or other part in a chamber may be raised to a temperature ranging from 70 to 200° C., 100° C. or more, or 180° C. or more. The substrate may be physically raised to be closer to the showerhead to increase the temperature of the second layer. Removing the second layer may also include etching the solid byproduct.

Embodiments may include forming a plurality of second features from a plurality of first features. The plurality of first features may include a plurality of trenches with openings with the same or different characteristic widths. If the characteristic widths are different, the second layer may fully block the opening of trenches with a characteristic width under at threshold but not block the opening of trenches with a characteristic width greater than or equal to the threshold. The second features formed from the plurality of first features would have openings with the same or different characteristic widths, depending on the widths of the first features.

Devices formed by these embodiments may have a similar breakdown voltage and threshold voltage as a device formed by the conventional method without a defect.

As shown in FIG. 4, embodiments of the present technology may include a method 400 of etching. Method 400 may include flowing a gas through a plasma to form plasma effluents (block 402). The gas, plasma, and plasma effluents may be any described herein.

Method 400 may also include reacting plasma effluents with a polysilicon layer defining a first trench (block 404). The first trench may include a first sidewall, a second sidewall, and a bottom. The first sidewall, the second sidewall, and the bottom may include the polysilicon layer. The polysilicon layer may be characterized by a first thickness on the first sidewall. The first thickness may be any thickness described herein.

Method 400 may further include forming a first solid layer from the reaction of the plasma effluents with the polysilicon layer (block 406). The polysilicon layer may be replaced by the first solid layer. The first solid layer may include (NH₄)₂SiF₆. The first solid layer may be characterized by a second thickness. The second thickness may be greater than or equal to the first thickness.

Method 400 may include removing the first solid layer to expose a remaining portion of the polysilicon layer (block 408). The remaining portion of the polysilicon layer may define a portion of a second trench. Removing the first solid layer may be any process described herein.

II. Anisotropic Removal

A. Process Flow

As characteristic dimensions decrease, the overhang at the top of a trench or via formed by the deposition of a layer may have a greater impact on processing and device performance. In some embodiments, the overhang at the top of a trench may be so severe as to create a seam or a void in otherwise filled trench. FIG. 5 illustrates a process for etching, which result in increased etching near the top of a feature and may reduce overhang. Polysilicon layer 502 may coat underlying layers and define a trench. In the leftmost figure of FIG. 5, polysilicon layer 502 is shown to conformally coat a trench. However, in some instances, polysilicon layer 502 may be characterized by a larger thickness at the top of the trench than in the middle of the trench—forming an overhang. Polysilicon layer 502 may contact layer 504 in the area defining the trench. Layer 504 may contact layer 506, which may be contact and be on top of substrate 508.

In the middle image of FIG. 5, a solid byproduct layer 520 is shown. Solid byproduct layer 520 is the result of a reaction of polysilicon layer 502 with etchants comprising nitrogen, hydrogen, and fluorine. Solid byproduct layer 520 may reduce the etchants reaching the bottom of the trench. Solid byproduct layer 520 may be any byproduct described herein. As a result, polysilicon layer 502 may have more etching near the top of the trench compared to the bottom of the trench, resulting in remaining polysilicon layer 522.

The rightmost image of FIG. 5 shows the structure after the removal of solid byproduct layer 520 by annealing or other removal techniques. Remaining polysilicon layer 522 defines the trench. If polysilicon is completely removed from the top of the trench, layer 504 may also define a portion of the trench. The resulting structure may not include an overhang. An additional layer may be deposited onto the structure, which may result in more vertical sidewalls without an overhang. This kind of profile modification capability can help to achieve seamless gap fill. While FIG. 5 shows an example of an anisotropic etch, anisotropic etch is not limited to FIG. 5. Anisotropic etch may also apply to the process described with FIG. 2.

B. Example Method

As shown in FIG. 6, embodiments of the present technology may include a method 600 of etching. Method 600 may include flowing a gas through a plasma to form plasma effluents (block 602). The gas, plasma, and plasma effluents may be any described herein.

Method 600 may also include reacting plasma effluents with a first layer defining a first trench (block 604). The first layer may be any first layer described herein. The first layer may be polysilicon layer 502 in FIG. 5. The first feature may include a first sidewall, a second sidewall, and a bottom. The first sidewall, the second sidewall, and the bottom may include the first layer. The first layer may be characterized by a first thickness at a first position on the first sidewall. The first thickness may be any thickness of a first layer described herein before reacting the first layer with plasma effluents. The first layer may be characterized by a second thickness at a second position above the first position on the first sidewall.

The first position may be located at the top of the second trench where the second trench becomes substantially perpendicular to the first sidewall. In some embodiments, the first position may be 10%, 20%, 30%, 40%, or 50% from the top of the second trench. The second position may be located at a location where immediately below the second position, the first layer does not contact the void defined by the second trench in a direction perpendicular to the first sidewall. For example, the second position may be above the bottom corner of the trench shown in the leftmost image in FIG. 5. In some embodiments, the second position may be 10%, 20%, 30%, 40%, or 50% from the bottom of the second trench. The first position and second position may refer to only a vertical location, using the orientation of the substrate in the figures.

Method 600 may further include forming a second layer from the reaction of the plasma effluents with the first layer (block 606). A portion of the first layer may be replaced by the second layer. The second layer may fill up the opening previously defined by the first trench. The second layer may be solid byproduct layer 520 in FIG. 5.

In addition, method 600 may include removing the second layer to expose a remaining portion of the first layer and to define a second trench (block 608). Removing the second layer may be by any removal technique described herein. The remaining portion of the first layer may be the remaining polysilicon layer 522 in FIG. 5. The remaining portion of the first layer may be characterized by a third thickness at the second position on the first sidewall. The remaining portion of the first layer may be characterized by a fourth thickness at the first position on the first sidewall. The fourth thickness may be greater than the third thickness. The third thickness may be the minimum thickness of the remaining portion of the first layer on the first sidewall. The remaining portion of the first layer may be characterized by a thickness that increases from the second position second position to the first position. The thickness may increase monotonically, or the thickness of the first layer may taper from the first position to the second position. The third thickness may not be greater than any thickness of the second layer at a location closer to the bottom of the second trench than the first position. The second layer may not form an overhang at the top of the second trench.

Method 600 may include taking the substrate out of the chamber and performing additional patterning and processing steps. Method 600 may include depositing a third layer on top of the remaining portion of the first layer to define a third trench.

III. Equipment

Processing chambers that may implement embodiments of the present invention may be included within processing platforms such as the Producer® Selectra™ etch system, available from Applied Materials, Inc. of Santa Clara, Calif.

FIG. 7 shows a top plan view of one embodiment of a processing tool 1000 of deposition, etching, baking, and curing chambers according to disclosed embodiments. In the figure, a pair of front opening unified pods (FOUPs) 1002 supply substrates of a variety of sizes that are received by robotic arms 1004 and placed into a low pressure holding area 1006 before being placed into one of the substrate processing chambers 1008 a-f, positioned in tandem sections 1009 a-c. A second robotic arm 1010 may be used to transport the substrate wafers from the holding area 1006 to the substrate processing chambers 1008 a-f and back. Each substrate processing chamber 1008 a-f, can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation, and other substrate processes.

The substrate processing chambers 1008 a-f may include one or more system components for depositing, annealing, curing and/or etching a film on the substrate wafer. In one configuration, two pairs of the processing chamber, e.g., 1008 c-d and 1008 e-f, may be used to deposit material on the substrate, and the third pair of processing chambers, e.g., 1008 a-b, may be used to etch the deposited film. In another configuration, all three pairs of chambers, e.g., 1008 a-f, may be configured to etch a film on the substrate. Any one or more of the processes described may be carried out in chamber(s) separated from the fabrication system shown in different embodiments. Films may be dielectric, protective, or other material. It will be appreciated that additional configurations of deposition, etching, annealing, and curing chambers for films are contemplated by processing tool 1000.

FIG. 8 shows a cross-sectional view of an exemplary process chamber section 2000 with partitioned plasma generation regions within the processing chamber. During film etching, e.g., silicon, polysilicon, silicon oxide, silicon nitride, silicon oxynitride, silicon oxycarbide, carbon-containing material, etc., a process gas may be flowed into the first plasma region 2015 through a gas inlet assembly 2005. A remote plasma system (RPS) unit 2001 may be included in the system, and may process a gas which then may travel through gas inlet assembly 2005. The inlet assembly 2005 may include two or more distinct gas supply channels where the second channel (not shown) may bypass the RPS unit 2001. Accordingly, in disclosed embodiments the precursor gases may be delivered to the processing chamber in an unexcited state. In another example, the first channel provided through the RPS may be used for the process gas and the second channel bypassing the RPS may be used for a treatment gas in disclosed embodiments. The process gases may be excited within the RPS unit 2001 prior to entering the first plasma region 2015. Accordingly, a fluorine-containing precursor, for example, may pass through RPS 2001 or bypass the RPS unit in disclosed embodiments. Various other examples encompassed by this arrangement will be similarly understood.

A cooling plate 2003, faceplate 2017, ion suppressor 2023, showerhead 2025, and a substrate support 2065, having a substrate 2055 disposed thereon, are shown and may each be included according to disclosed embodiments. The pedestal 2065 may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate. This configuration may allow the substrate 2055 temperature to be cooled or heated to maintain relatively low temperatures, such as between about −20° C. to about 200° C., or therebetween. The heat exchange fluid may comprise ethylene glycol and/or water. The wafer support platter of the pedestal 2065, which may comprise aluminum, ceramic, or a combination thereof, may also be resistively heated in order to achieve relatively high temperatures, such as from up to or about 100° C. to above or about 1100° C., using an embedded resistive heater element. The heating element may be formed within the pedestal as one or more loops, and an outer portion of the heater element may run adjacent to a perimeter of the support platter, while an inner portion runs on the path of a concentric circle having a smaller radius. The wiring to the heater element may pass through the stem of the pedestal 2065, which may be further configured to rotate.

The faceplate 2017 may be pyramidal, conical, or of another similar structure with a narrow top portion expanding to a wide bottom portion. The faceplate 2017 may additionally be flat as shown and include a plurality of through-channels used to distribute process gases. Plasma generating gases and/or plasma excited species, depending on use of the RPS 2001, may pass through a plurality of holes in faceplate 2017 for a more uniform delivery into the first plasma region 2015.

Exemplary configurations may include having the gas inlet assembly 2005 open into a gas supply region 2058 partitioned from the first plasma region 2015 by faceplate 2017 so that the gases/species flow through the holes in the faceplate 2017 into the first plasma region 2015. Structural and operational features may be selected to prevent significant backflow of plasma from the first plasma region 2015 back into the supply region 2058, gas inlet assembly 2005, and fluid supply system (not shown). The structural features may include the selection of dimensions and cross-sectional geometries of the apertures in faceplate 2017 to deactivate back-streaming plasma. The operational features may include maintaining a pressure difference between the gas supply region 2058 and first plasma region 2015 that maintains a unidirectional flow of plasma through the showerhead 2025. The faceplate 2017, or a conductive top portion of the chamber, and showerhead 2025 are shown with an insulating ring 2020 located between the features, which allows an AC potential to be applied to the faceplate 2017 relative to showerhead 2025 and/or ion suppressor 2023. The insulating ring 2020 may be positioned between the faceplate 2017 and the showerhead 2025 and/or ion suppressor 2023 enabling a capacitively coupled plasma (CCP) to be formed in the first plasma region. A baffle (not shown) may additionally be located in the first plasma region 2015, or otherwise coupled with gas inlet assembly 2005, to affect the flow of fluid into the region through gas inlet assembly 2005.

The ion suppressor 2023 may comprise a plate or other geometry that defines a plurality of apertures throughout the structure that are configured to suppress the migration of charged species (e.g., ions) out of the plasma excitation region 2015 while allowing uncharged neutral or radical species to pass through the ion suppressor 2023 into an activated gas delivery region between the suppressor and the showerhead. In disclosed embodiments, the ion suppressor 2023 may comprise a perforated plate with a variety of aperture configurations. These uncharged species may include highly reactive species that are transported with less reactive carrier gas through the apertures. As noted above, the migration of ionic species through the holes may be reduced, and in some instances completely suppressed. Controlling the amount of ionic species passing through the ion suppressor 2023 may provide increased control over the gas mixture brought into contact with the underlying wafer substrate, which in turn may increase control of the deposition and/or etch characteristics of the gas mixture. For example, adjustments in the ion concentration of the gas mixture can significantly alter its etch selectivity. In alternative embodiments in which deposition is performed, it can also shift the balance of conformal-to-flowable style depositions for dielectric materials, carbon-containing materials, and other materials.

The plurality of holes in the ion suppressor 2023 may be configured to control the passage of the activated gas, i.e., the ionic, radical, and/or neutral species, through the ion suppressor 2023. For example, the aspect ratio of the holes, or the hole diameter to length, and/or the geometry of the holes may be controlled so that the flow of ionically-charged species in the activated gas passing through the ion suppressor 2023 is reduced. The holes in the ion suppressor 2023 may include a tapered portion that faces the plasma excitation region 2015, and a cylindrical portion that faces the showerhead 2025. The cylindrical portion may be shaped and dimensioned to control the flow of ionic species passing to the showerhead 2025. An adjustable electrical bias may also be applied to the ion suppressor 2023 as an additional means to control the flow of ionic species through the suppressor.

The ion suppression element 2023 may function to reduce or eliminate the amount of ionically-charged species traveling from the plasma generation region to the substrate. Uncharged neutral and radical species may still pass through the openings in the ion suppressor to react with the substrate. It should be noted that the complete elimination of ionically-charged species in the reaction region surrounding the substrate is not always the desired goal. In many instances, ionic species are required to reach the substrate in order to perform the etch and/or deposition process. In these instances, the ion suppressor may help to control the concentration of ionic species in the reaction region at a level that assists the process.

Showerhead 2025 in combination with ion suppressor 2023 may allow a plasma present in chamber plasma region 2015 to avoid directly exciting gases in substrate processing region 2033, while still allowing excited species to travel from chamber plasma region 2015 into substrate processing region 2033. In this way, the chamber may be configured to prevent the plasma from contacting a substrate 2055 being etched. This may advantageously protect a variety of intricate structures and films patterned on the substrate, which may be damaged, dislocated, or otherwise warped if directly contacted by a generated plasma. Additionally, when plasma is allowed to contact the underlying material exposed by trenches, such as the etch stop, the rate at which the underlying material etches may increase.

The processing system may further include a power supply 2040 electrically coupled with the processing chamber to provide electric power to the faceplate 2017, ion suppressor 2023, showerhead 2025, and/or pedestal 2065 to generate a plasma in the first plasma region 2015 or processing region 2033. The power supply may be configured to deliver an adjustable amount of power to the chamber depending on the process performed. Such a configuration may allow for a tunable plasma to be used in the processes being performed. Unlike a remote plasma unit, which is often presented with on or off functionality, a tunable plasma may be configured to deliver a specific amount of power to the plasma region 2015. This in turn may allow development of particular plasma characteristics such that precursors may be dissociated in specific ways to enhance the etching profiles produced by these precursors.

A plasma may be ignited either in chamber plasma region 2015 above showerhead 2025 or substrate processing region 2033 below showerhead 2025. A plasma may be present in chamber plasma region 2015 to produce radical-fluorine precursors from an inflow of a fluorine-containing precursor. An AC voltage typically in the radio frequency (RF) range may be applied between the conductive top portion of the processing chamber, such as faceplate 2017, and showerhead 2025 and/or ion suppressor 2023 to ignite a plasma in chamber plasma region 2015 during deposition. An RF power supply may generate a high RF frequency of 13.56 MHz but may also generate other frequencies alone or in combination with the 13.56 MHz frequency.

Plasma power can be of a variety of frequencies or a combination of multiple frequencies. In the exemplary processing system the plasma may be provided by RF power delivered to faceplate 2017 relative to ion suppressor 2023 and/or showerhead 2025. The RF power may be between about 10 watts and about 2000 watts, between about 100 watts and about 2000 watts, between about 200 watts and about 1500 watts, or between about 200 watts and about 1000 watts in different embodiments. The RF frequency applied in the exemplary processing system may be low RF frequencies less than about 200 kHz, high RF frequencies between about 10 MHz and about 15 MHz, or microwave frequencies greater than or about 1 GHz in different embodiments. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the remote plasma region.

The top plasma region 2015 may be left at low or no power when a bottom plasma in the substrate processing region 2033 is turned on to, for example, cure a film or clean the interior surfaces bordering substrate processing region 2033. A plasma in substrate processing region 2033 may be ignited by applying an AC voltage between showerhead 2025 and the pedestal 2065 or bottom of the chamber. A cleaning gas may be introduced into substrate processing region 2033 while the plasma is present.

A fluid, such as a precursor, for example a fluorine-containing precursor, may be flowed into the processing region 2033 by embodiments of the showerhead described herein. Excited species derived from the process gas in the plasma region 2015 may travel through apertures in the ion suppressor 2023, and/or showerhead 2025 and react with an additional precursor flowing into the processing region 2033 from a separate portion of the showerhead. Alternatively, if all precursor species are being excited in plasma region 2015, no additional precursors may be flowed through the separate portion of the showerhead. Little or no plasma may be present in the processing region 2033. Excited derivatives of the precursors may combine in the region above the substrate and, on occasion, on the substrate to etch structures or remove species on the substrate in disclosed applications.

Exciting the fluids in the first plasma region 2015 directly, or exciting the fluids in the RPS unit 2001, may provide several benefits. The concentration of the excited species derived from the fluids may be increased within the processing region 2033 due to the plasma in the first plasma region 2015. This increase may result from the location of the plasma in the first plasma region 2015. The processing region 2033 may be located closer to the first plasma region 2015 than the remote plasma system (RPS) 2001, leaving less time for the excited species to leave excited states through collisions with other gas molecules, walls of the chamber, and surfaces of the showerhead.

The uniformity of the concentration of the excited species derived from the process gas may also be increased within the processing region 2033. This may result from the shape of the first plasma region 2015, which may be more similar to the shape of the processing region 2033. Excited species created in the RPS unit 2001 may travel greater distances in order to pass through apertures near the edges of the showerhead 2025 relative to species that pass through apertures near the center of the showerhead 2025. The greater distance may result in a reduced excitation of the excited species and, for example, may result in a slower growth rate near the edge of a substrate. Exciting the fluids in the first plasma region 2015 may mitigate this variation for the fluid flowed through RPS 2001.

The processing gases may be excited in the RPS unit 2001 and may be passed through the showerhead 2025 to the processing region 2033 in the excited state. Alternatively, power may be applied to the first processing region to either excite a plasma gas or enhance an already excited process gas from the RPS. While a plasma may be generated in the processing region 2033, a plasma may alternatively not be generated in the processing region. In one example, the only excitation of the processing gas or precursors may be from exciting the processing gases in the RPS unit 2001 to react with the substrate 2055 in the processing region 2033.

In addition to the fluid precursors, there may be other gases introduced at varied times for varied purposes, including carrier gases to aid delivery. A treatment gas may be introduced to remove unwanted species from the chamber walls, the substrate, the deposited film and/or the film during deposition. A treatment gas may be excited in a plasma and then used to reduce or remove residual content inside the chamber. In other disclosed embodiments the treatment gas may be used without a plasma. When the treatment gas includes water vapor, the delivery may be achieved using a mass flow meter (MFM), mass flow controller (MFC), an injection valve, or by commercially available water vapor generators. The treatment gas may be introduced to the processing region 2033, either through the RPS unit or bypassing the RPS units, and may further be excited in the first plasma region.

The specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of embodiments of the invention. However, other embodiments of the invention may be directed to specific embodiments relating to each individual aspect, or specific combinations of these individual aspects.

The above description of example embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above.

In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.

Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Additionally, details of any specific embodiment may not always be present in variations of that embodiment or may be added to other embodiments.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a method” includes a plurality of such methods and reference to “the layer” includes reference to one or more layers and equivalents thereof known to those skilled in the art, and so forth. The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practice within the scope of the appended claims.

All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes. None is admitted to be prior art. 

What is claimed is:
 1. A method of etching, the method comprising: flowing a gas through a plasma to form plasma effluents; reacting plasma effluents with a first layer defining a first feature, wherein: the first feature comprises a first sidewall, a second sidewall, and a first bottom, the first sidewall, the second sidewall, and the bottom comprise the first layer, and the first layer is characterized by a first thickness on the first sidewall; forming a second layer from the reaction of the plasma effluents with the first layer to define a third feature, wherein: the third feature comprises a third sidewall, a fourth sidewall, and a second bottom, the first layer is replaced by the second layer, the third sidewall, the fourth sidewall, and the second bottom comprise the second layer, the first sidewall is replaced by the third sidewall, the second layer is characterized by a second thickness on the third sidewall, and the second thickness is greater than or equal to the first thickness; and removing the second layer to expose a third layer, the third layer defining a second feature.
 2. The method of claim 1, wherein: the first feature is a trench or via characterized by a height, the height is a first height before reacting plasma effluents with the first layer, and forming the second layer comprises reducing the height of the trench or via from the first height to a second height.
 3. The method of claim 1, wherein the second feature is a trench or via.
 4. The method of claim 1, wherein reacting plasma effluents with the first layer is at a pressure greater than or equal to 1 Torr.
 5. The method of claim 1, wherein reacting plasma effluents with the first layer is at a temperature of less than or equal to 70° C.
 6. The method of claim 1, wherein the first layer comprises silicon.
 7. The method of claim 1, wherein the second layer comprises (NH₄)₂SiF₆.
 8. The method of claim 1, wherein the second layer comprises N—H and Si—F bonds.
 9. The method of claim 1, wherein the gas comprises: a fluorine-containing gas, and a hydrogen-containing gas, wherein: the fluorine-containing gas comprises NF₃, F₂, or HF, and the hydrogen-containing gas comprises H₂, NH₃, or an amine.
 10. The method of claim 1, wherein the first thickness is in a range from 15 Angstroms to 300 Angstroms.
 11. The method of claim 1, wherein the first layer comprises polysilicon.
 12. The method of claim 11, wherein the second layer comprises N—H and Si—F bonds.
 13. The method of claim 11, wherein the second layer comprises (NH₄)₂SiF₆.
 14. A method of etching, the method comprising: flowing a gas through a plasma to form plasma effluents; reacting plasma effluents with a first layer defining a first trench, wherein: the first trench comprises a first sidewall, a second sidewall, and a bottom, the first sidewall, the second sidewall, and the bottom comprise the first layer, the first layer is characterized by a first thickness at a first position on the first sidewall, and the first layer is characterized by a second thickness at a second position above the first position on the first sidewall; forming a second layer from the reaction of the plasma effluents with the first layer, wherein a portion of the first layer is replaced by a second layer; and removing the second layer to expose a remaining portion of the first layer and to define a second trench, wherein: the remaining portion of the first layer is characterized by a third thickness at the second position on the first sidewall, the remaining portion of the first layer is characterized by a fourth thickness at the first position on the first sidewall, and the fourth thickness is greater than the third thickness.
 15. The method of claim 14, wherein the third thickness is the minimum thickness of the remaining portion of the first layer on the first sidewall.
 16. The method of claim 14, wherein: the first position is located at the top of the second trench where the second trench becomes substantially perpendicular to the first sidewall, and the second position is located at a location where immediately below the second position, the first layer does not contact a void defined by the second trench in a direction perpendicular to the first sidewall.
 17. The method of claim 14, wherein the first layer comprises polysilicon.
 18. The method of claim 17, wherein the second layer comprises N—H and Si—F bonds.
 19. The method of claim 18, wherein the second layer comprises (NH₄)₂SiF₆.
 20. A method of etching, the method comprising: flowing a gas through a plasma to form plasma effluents; reacting plasma effluents with a polysilicon layer defining a first trench, wherein: the first trench comprises a first sidewall, a second sidewall, and a bottom, the first sidewall, the second sidewall, and the bottom comprise the polysilicon layer, and the polysilicon layer is characterized by a first thickness on the first sidewall; forming a first solid layer from the reaction of the plasma effluents with the polysilicon layer, wherein: the polysilicon layer is replaced by the first solid layer, the first solid layer comprises (NH₄)₂SiF₆, the first solid layer is characterized by a second thickness, and the second thickness is greater than or equal to the first thickness; and removing the first solid layer to expose a second solid layer, the second solid layer defining a portion of a second trench. 